The AVR is linked to both the main stator windings and the exciter field windings to form a closed loop control of the output voltage. As well as being powered from the main stator it also derives a sample voltage from the output windings for voltage control purposes. From this sample voltage the unit controls the power fed to the exciter field and hence the main field to maintain the machine output voltage within the specified limits. It will compensate for load, speed and temperature of the generator. The frequency measuring circuit continually monitors the generator output and provides under speed protection of the excitation system. A manual adjustment is provided for factory setting of the under frequency roll off point. This can easily be changed if necessary.
